This invention relates generally to electromagnetic field intensity measurement apparatus and more particularly to means for use with a conventional radio receiver to measure weak electromagnetic fields of unknown orientation, for example, leakage emanations from electronic equipment placed within a shielded enclosure.
One typical technique uses a high resistance transmission line such as carbon impregnated plastic to convey the detected antenna signal to a high impedance DC readout meter. This type of probe is often used to map intense fields approaching the hazard level and search for possible interference over a range of 0.1 to 1000 volts per meter. In this type of probe, the composite RF pickup is detected by a diode across the center gap of the dipole; however, no attempt is made to measure the amplitude as a function of frequency. Another technique utilizes an active antenna located in an intense field, suitably coupled to a conventional receiver remotely located from the antenna for measuring the amplitude of the field.